How do/should I wish a former love interest congratulations on her engagement?

I'm talking about the same girl from the last question I posted. The thing is our relationship/friendship didn't end well, i kept pestering her for some type of closure which she finally gave me but politely asked that I don't contact her anymore. she didn't do this in a malicious way just in a case closed business manner. I haven't spoken to her since and to tell you the truth i am a little bitter and i can't say whole heartedly that i am happy for her, mostly b/c i don't know the guy that well. another former love interest got engaged 3 weeks ago and i couldn't be more happy mostly b/c i got to know them as a couple and i am very excited for both of them. I can't say the same for her b/c i don't know enough about the situation. should i just keep up the non-correspondance or take the "high road" and send my congrats?